First gamma-ray pulsar outside our own galaxy found in the Large Magellanic Cloud.

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Pulsars are rapidly spinning neutron stars, which create pulsed emissions as their magnetic fields sweep across the line of sight with Earth. Generally, these are detected as radio wavelengths. But in rare cases, the environment around the pulsar is energetic enough to create gamma rays. Now, researchers have used these gamma rays to spot the first one of these seen outside our own galaxy. The pulsar is the most luminous ever seen at these wavelengths, with each pulse outputting 1036 ergs—a bit over 1015 megatons.

The discovery was made possible by two things: the Fermi Gamma-ray Space Telescope and time. Gamma rays are so energetic that it's difficult to focus them, so you can only get a rough idea of what direction they're coming from. But, with time, Fermi has been able to identify a gamma ray source in the Tarantula nebula, located in one of the Milky Way's satellite galaxies, the Large Magellanic Cloud.

This still wasn't precise enough to identify a single object, but a couple of pulsars had previously been identified in the nebula. By matching the gamma ray pulses to the timing of pulses at other wavelengths, the Fermi team was able to identify the source as PSR J0540–6919, the remnant of a supernova that occurred roughly 1,100 years ago. The amount of energy in the pulses makes it the most energetic gamma ray pulsar yet discovered, displacing the neutron star at the center of the Crab Nebula.

How does a rotating star manage to produce something as energetic as gamma radiation? Neutron stars start out spinning rapidly and have intense magnetic fields (a consequence of having the mass of the Sun crammed into a sphere roughly 10km across). The spin creates curved magnetic fields that help direct energetic particles in the environment—and, given it's in a supernova remnant, there are a lot of energetic particles around.

As these particles get accelerated across a curved path, they shed energy as photons. And, once this radiation gets intense enough, some of the energy is converted back into matter in the form of electron/positron pairs. These get accelerated as well, producing more photons and generating a cascade.

The energy released through the process gradually slows the pulsar down. But, since this one is only about 1,000 years old, it's still extremely energetic.

The authors suggest observations of this can provide a clearer picture of the complex environment above neutron stars, including the area (called a light cylinder) where anything that's matching the star's rotation has to be moving at the speed of light.

Out of curiosity, this doesn't take into account the fact the time the light took to get here in order to make these observations, right?

I ask this because the Large Magellanic Cloud is 163 000 light-years away, so doesn't this mean the event actually occurred at least 164 100 years ago?

This is something that has had me confused for a long time.

You're correct. It would be 1100 years ago as visible to us here on earth. We have no way of knowing what has happened to it in the last 164000 earth years. Though that's how everything works at such scales. We're looking back in time pretty much everywhere. Even our own sun is 8 minutes in the past. Everything is relative to the viewer. You would observe a "different" snapshot in time of the universe if you were in another solar system or galaxy.

On an unrelated note, "outputting 1036 ergs—a bit over 1015 megatons." is that straight from the paper? I haven't checked out the actual pub yet but, megatons? Megatons of what? TNT? Why is this in ergs either? Why not GeV?

10^15 megatons of what? TNT? That doesn't make any sense. This isn't an explosion, its a stream of gamma rays.

Gamma rays are a form of energy. The rate at which they are produced gives a "power".

It always amuses me that astrophysicists use ergs to measure the power of some of the most powerful things in the universe when "one erg is approximately the amount of work done (or energy consumed) by one common house fly performing one "push up", the leg-bending dip that brings its mouth to the surface on which it stands and back up." https://en.wikipedia.org/wiki/Erg

You're correct. It would be 1100 years ago as visible to us here on earth. We have no way of knowing what has happened to it in the last 164000 earth years. Though that's how everything works at such scales. We're looking back in time pretty much everywhere. Even our own sun is 8 minutes in the past. Everything is relative to the viewer. You would observe a "different" snapshot in time of the universe if you were in another solar system or galaxy.

10^15 megatons of what? TNT? That doesn't make any sense. This isn't an explosion, its a stream of gamma rays.

I can't quote myself, but to follow on from my previous post:

"Gamma rays are a form of energy. The rate at which they are produced gives a "power"."

The pulse lasts for a certain duration and thus you can convert the power in ergs to a quantity of energy. A "megaton" refers to the equivalent energy released in an explosion of a million tons of conventional explosive. Thus the figure quoted is the energy in gamma rays released in that pulse. Nuclear weapons also release a lot of energy in form of gamma rays (and across the electromagnetic spectrum in visible light in addition to the energy that creates the shockwave).

Pro Tip: remember if you are going to plot a parabolic path around it, make sure you are at the exact center of mass at perigee otherwise the tide created by the gravity and extremely sharp gravitational gradient might slam you into the nose of your ship and crush you into a bloody pulp.

Out of curiosity, this doesn't take into account the fact the time the light took to get here in order to make these observations, right?

I ask this because the Large Magellanic Cloud is 163 000 light-years away, so doesn't this mean the event actually occurred at least 164 100 years ago?

This is something that has had me confused for a long time.

Something I don't get about some ARS readers. Generally the community is respectful, but sometimes some of you can be real asses.

Case in point: Who is the ass that downvoted a perfectly legitimate and well stated question? It's clearly an attempt to understand. If your kid (assuming you can find some to procreate with) were to ask you a "dumb" question would you tell them they are an idiot? People seeking knowledge should be applauded, not jeered. But hey, whatever it takes to make you feel good about yourselves, right?

So assuming that's "of TNT", that's a unbelievable amount of energy per pulse (and I'm guessing it is pulsing hundreds of times per second). Edit: Turns out the paper says 10^36 ergs per second, which makes it a bit less insane but still crazy.

For people having issues visualizing that, the biggest bomb ever set off was Tsar Bomba, which was 50 megatons and could have theoretically been scaled to 100 megatons, or 10^2 megatons. This is 10^11 times bigger, or 100 billion times as much energy. Every second.

10^15 megatons of what? TNT? That doesn't make any sense. This isn't an explosion, its a stream of gamma rays.

I can't quote myself, but to follow on from my previous post:

"Gamma rays are a form of energy. The rate at which they are produced gives a "power"."

The pulse lasts for a certain duration and thus you can convert the power in ergs to a quantity of energy. A "megaton" refers to the equivalent energy released in an explosion of a million tons of conventional explosive. Thus the figure quoted is the energy in gamma rays released in that pulse. Nuclear weapons also release a lot of energy in form of gamma rays (and across the electromagnetic spectrum in visible light in addition to the energy that creates the shockwave).

Out of curiosity, this doesn't take into account the fact the time the light took to get here in order to make these observations, right?

I ask this because the Large Magellanic Cloud is 163 000 light-years away, so doesn't this mean the event actually occurred at least 164 100 years ago?

This is something that has had me confused for a long time.

Something I don't get about some ARS readers. Generally the community is respectful, but sometimes some of you can be real asses.

Case in point: Who is the ass that downvoted a perfectly legitimate and well stated question? It's clearly an attempt to understand. If your kid (assuming you can find some to procreate with) were to ask you a "dumb" question would you tell them they are an idiot? People seeking knowledge should be applauded, not jeered. But hey, whatever it takes to make you feel good about yourselves, right?

Down voting has kind of become an "I disagree with your point of view" or "you shouldnt be here if you don't know as much me" statement. If you're not signed in, the minority view isn't even viewable anymore. It's kind of a shame because instead of heeding devil's advocate people just down vote it and flip out.

For people having issues visualizing that, the biggest bomb ever set off was Tsar Bomba, which was 50 megatons and could have theoretically been scaled to 100 megatons, or 10^2 megatons.

Another way to put some scale to that is to say that 10^36 ergs is roughly equivalent to the total energy put out by our sun during a period of 250 seconds.And that's all compressed into a single pulse.

10^15 megatons of what? TNT? That doesn't make any sense. This isn't an explosion, its a stream of gamma rays.

Gamma rays are a form of energy. The rate at which they are produced gives a "power".

It always amuses me that astrophysicists use ergs to measure the power of some of the most powerful things in the universe when "one erg is approximately the amount of work done (or energy consumed) by one common house fly performing one "push up", the leg-bending dip that brings its mouth to the surface on which it stands and back up." https://en.wikipedia.org/wiki/Erg

And here I was thinking that the term "erg" was derived from the sound one makes when spending energy doing said work. Imagine that.

Out of curiosity, this doesn't take into account the fact the time the light took to get here in order to make these observations, right?

I ask this because the Large Magellanic Cloud is 163 000 light-years away, so doesn't this mean the event actually occurred at least 164 100 years ago?

This is something that has had me confused for a long time.

Something I don't get about some ARS readers. Generally the community is respectful, but sometimes some of you can be real asses.

Case in point: Who is the ass that downvoted a perfectly legitimate and well stated question? It's clearly an attempt to understand. If your kid (assuming you can find some to procreate with) were to ask you a "dumb" question would you tell them they are an idiot? People seeking knowledge should be applauded, not jeered. But hey, whatever it takes to make you feel good about yourselves, right?

We are the Ars Technica comments section. You will be assholinated. Your physical and technological distinctiveness will be added to our own. Your inquisitiveness will be adapted to service our ego. Resistance is futile...

Out of curiosity, this doesn't take into account the fact the time the light took to get here in order to make these observations, right?

I ask this because the Large Magellanic Cloud is 163 000 light-years away, so doesn't this mean the event actually occurred at least 164 100 years ago?

This is something that has had me confused for a long time.

Something I don't get about some ARS readers. Generally the community is respectful, but sometimes some of you can be real asses.

Case in point: Who is the ass that downvoted a perfectly legitimate and well stated question? It's clearly an attempt to understand. If your kid (assuming you can find some to procreate with) were to ask you a "dumb" question would you tell them they are an idiot? People seeking knowledge should be applauded, not jeered. But hey, whatever it takes to make you feel good about yourselves, right?

This topic comes up pretty often. I made a comment once that, no matter how good a post is, there is always one ass that will downvote it.

Pro Tip: remember if you are going to plot a parabolic path around it, make sure you are at the exact center of mass at perigee otherwise the tide created by the gravity and extremely sharp gravitational gradient might slam you into the nose of your ship and crush you into a bloody pulp.

10^15 megatons of what? TNT? That doesn't make any sense. This isn't an explosion, its a stream of gamma rays.

"Megatons" is usually understood as megatons of TNT.

So in a single pulse, this thing emits the same amount of energy as would be released by detonating 10e15 MT of TNT.

Per the first unit conversion calculator I could find, that's 4.184e+31 Joules.

That's...a lot. Don't think you'd want to be in the neighborhood.

Is there some way you can tie that to something understandable, like a warm summer afternoon, or maybe a Megadeth concert?

As stated a few posts up, it's the equivalent of the total power output of the sun for about 4 minutes. And that's happening about 20 times every second. Edit: Thanks Electrostatus, I thought they were saying that was the power of the pulses.

According to this page, it's period is 0.0503771068690000 seconds, and if my math is correct it was spinning about 30% faster 1100 years ago. (And it will take ~64,000 years to slow down to 1 rotation per second)

We are seeing this neutron star at a state 1100 years after it supernova'd. 1100 years ago, someone looking at the LMC may have seen the explosion.

It doesn't really matter if it "really happened" 163000 years ago, because we can't see what it's like "now"

Instead of saying it blew up 164100 years ago, and then looks like this 163000 years ago, we just use human time scale.

There is no absolute time scale, and that thing is dense enough and spinning fast enough that it's own clock is running slow.

Even using our time scale, 1100 years have past for us, but [insert real math] somewhat less for this stars clock

Plus saying "164100 years ago" would be an example of false precision because we don't know the distance and thus time-of-flight of photons from the pulsar that closely. Time since we would have observed an event, and distance to that event, are separate measurements with separate error.

An even more extreme example - the Crab Nebula is 6500 +/- 1600 ly away. It is believed that the Crab Nebula is the remnant of the naked-eye-visible supernova of 1054. So time since we witnessed it is much more tightly constrained than how far away it is. Trying to combine the two figures would mean erasing our rather specific knowledge of when it exploded.

10^15 megatons of what? TNT? That doesn't make any sense. This isn't an explosion, its a stream of gamma rays.

"Megatons" is usually understood as megatons of TNT.

So in a single pulse, this thing emits the same amount of energy as would be released by detonating 10e15 MT of TNT.

Per the first unit conversion calculator I could find, that's 4.184e+31 Joules.

That's...a lot. Don't think you'd want to be in the neighborhood.

Is there some way you can tie that to something understandable, like a warm summer afternoon, or maybe a Megadeth concert?

Depends. Would you find it more intuitive to visualize the energy released by simultaneously detonating 100 trillion silo-busting thermonuclear bombs, twenty times a second? How about the intensity of the resulting pulse if you could channel that energy into a narrow beam?

10^15 megatons of what? TNT? That doesn't make any sense. This isn't an explosion, its a stream of gamma rays.

"Megatons" is usually understood as megatons of TNT.

So in a single pulse, this thing emits the same amount of energy as would be released by detonating 10e15 MT of TNT.

Per the first unit conversion calculator I could find, that's 4.184e+31 Joules.

That's...a lot. Don't think you'd want to be in the neighborhood.

Is there some way you can tie that to something understandable, like a warm summer afternoon, or maybe a Megadeth concert?

Assuming all amplification gear is tuned to 11 and the featured band doesn't get lost behind stage, what we have here is approximately 10^30 Spinal Tap concerts, which is roughly the amount of energy required to leave you deaf, drunk, half blind, and quivering while still pointing the devil horns towards stage while some underage girl who snuck in to the venue throws up on your boot.

For people having issues visualizing that, the biggest bomb ever set off was Tsar Bomba, which was 50 megatons and could have theoretically been scaled to 100 megatons, or 10^2 megatons.

When they say "energy of pulse", do they mean "energy released during the time the light is visible to terran observers"? (It is actually releasing energy constantly throughout its rotation.) Or do they mean per rotation? And are they including the beam on the other side?

An even more extreme example - the Crab Nebula is 6500 +/- 1600 ly away. It is believed that the Crab Nebula is the remnant of the naked-eye-visible supernova of 1054. So time since we witnessed it is much more tightly constrained than how far away it is. Trying to combine the two figures would mean erasing our rather specific knowledge of when it exploded.

Out of curiosity, this doesn't take into account the fact the time the light took to get here in order to make these observations, right?

I ask this because the Large Magellanic Cloud is 163 000 light-years away, so doesn't this mean the event actually occurred at least 164 100 years ago?

This is something that has had me confused for a long time.

Something I don't get about some ARS readers. Generally the community is respectful, but sometimes some of you can be real asses.

Case in point: Who is the ass that downvoted a perfectly legitimate and well stated question? It's clearly an attempt to understand. If your kid (assuming you can find some to procreate with) were to ask you a "dumb" question would you tell them they are an idiot? People seeking knowledge should be applauded, not jeered. But hey, whatever it takes to make you feel good about yourselves, right?

Gentle reminder that questioning someone's ability to procreate is neither kind nor respectful. It's easy to run off the rails, yes? I mean, we all do it from time to time. I think it is acknowledging it that makes all the difference.

For people having issues visualizing that, the biggest bomb ever set off was Tsar Bomba, which was 50 megatons and could have theoretically been scaled to 100 megatons, or 10^2 megatons.

Another way to put some scale to that is to say that 10^36 ergs is roughly equivalent to the total energy put out by our sun during a period of 250 seconds.And that's all compressed into a single pulse.

That is a much more useful way of putting the output. Then multiply by the number of pulses per second, and some geometric correction factor, and we can compare the output directly to that of the sun, as it is continuous output that we observe in pulsatile fashion. Then to put it in the other perspective, one (not me) can estimate what percentage of the preceding supernova explosion energy output this is.

This topic comes up pretty often. I made a comment once that, no matter how good a post is, there is always one ass that will downvote it.I got one downvote.

I've also noticed the "lone downvote" phenomenon and wondered if it's the same person going though each comment; and if there's a high upvote with no downvotes, adds one to keep balance in the universe…or maybe, as you say, they're just an ass.

10^15 megatons of what? TNT? That doesn't make any sense. This isn't an explosion, its a stream of gamma rays.

"Megatons" is usually understood as megatons of TNT.

So in a single pulse, this thing emits the same amount of energy as would be released by detonating 10e15 MT of TNT.

Per the first unit conversion calculator I could find, that's 4.184e+31 Joules.

That's...a lot. Don't think you'd want to be in the neighborhood.

Is there some way you can tie that to something understandable, like a warm summer afternoon, or maybe a Megadeth concert?

Assuming all amplification gear is tuned to 11 and the featured band doesn't get lost behind stage, what we have here is approximately 10^30 Spinal Tap concerts, which is roughly the amount of energy required to leave you deaf, drunk, half blind, and quivering while still pointing the devil horns towards stage while some underage girl who snuck in to the venue throws up on your boot.

10^15 megatons of what? TNT? That doesn't make any sense. This isn't an explosion, its a stream of gamma rays.

"Megatons" is usually understood as megatons of TNT.

So in a single pulse, this thing emits the same amount of energy as would be released by detonating 10e15 MT of TNT.

Per the first unit conversion calculator I could find, that's 4.184e+31 Joules.

That's...a lot. Don't think you'd want to be in the neighborhood.

Is there some way you can tie that to something understandable, like a warm summer afternoon, or maybe a Megadeth concert?

Assuming all amplification gear is tuned to 11 and the featured band doesn't get lost behind stage, what we have here is approximately 10^30 Spinal Tap concerts, which is roughly the amount of energy required to leave you deaf, drunk, half blind, and quivering while still pointing the devil horns towards stage while some underage girl who snuck in to the venue throws up on your boot.

So you're saying it could be louder?

Yes, after all it's only 0.3 of the energy output of the typical Disaster Area concert. Queue the supernova ship...

Pro Tip: remember if you are going to plot a parabolic path around it, make sure you are at the exact center of mass at perigee otherwise the tide created by the gravity and extremely sharp gravitational gradient might slam you into the nose of your ship and crush you into a bloody pulp.

Out of curiosity, this doesn't take into account the fact the time the light took to get here in order to make these observations, right?

I ask this because the Large Magellanic Cloud is 163 000 light-years away, so doesn't this mean the event actually occurred at least 164 100 years ago?

This is something that has had me confused for a long time.

Something I don't get about some ARS readers. Generally the community is respectful, but sometimes some of you can be real asses.

Case in point: Who is the ass that downvoted a perfectly legitimate and well stated question? It's clearly an attempt to understand. If your kid (assuming you can find some to procreate with) were to ask you a "dumb" question would you tell them they are an idiot? People seeking knowledge should be applauded, not jeered. But hey, whatever it takes to make you feel good about yourselves, right?

It's obviously someone who thought it was a megaton of kittens (or puppies) and didn't want someone else to answer and shatter that illusion.

Pro Tip: remember if you are going to plot a parabolic path around it, make sure you are at the exact center of mass at perigee otherwise the tide created by the gravity and extremely sharp gravitational gradient might slam you into the nose of your ship and crush you into a bloody pulp.

In that case: drinks all 'round just prior to perigee!

Just out of curiosity I'm wondering if anyone got the reference?

Certainly did - classic Niven, with Beowulf Schaeffer. Loved those books, still do - looking for a complete collection of Known Space in digital format, but still missing some short stories...

A sphere roughly 10 km across, and it's period is approximately 0.05 seconds, so if there was a fly sitting at the equator, how fast would it be travelling?

Let's see, the circumference would be 2 π r. Let's state the radius in meters: 5000 so we get a circumference of ~31,416 meters. Then every 0.05 seconds the fly travels 31,416 m. In 1 second, it travels 31,416 / 0.05, or about 628,319 m / s. Now the speed of light is 299,792,458 m / s, so lets see how the fly's velocity compares to the the speed of light. 100 x 628,319 / 299,792,458 = ~0.21 percent. Then the fly is travelling at 0.21 percent the speed of light.

Now the first time I did the calculation I got some ridiculous error making the fly travel at a superluminal velocity. A fraction of one percent the speed of light isn't nearly quite as impressive as I thought it would be. However, we can safely say that if the fly survives the radiation and crushing gravity for the duration of the period I measured its velocity, it will get seriously dizzy.

Now we got that out of the way, I have a far more interesting question. What is the density of that neutron star? Now that question is much easier to answer actually, because the question is merely rhetorical, to make a point. We know that a neutron star is so dense that a teaspoon of neutron star material would weigh about 10 million tons. The collapsed star is so dense that electrons and protons do not exist separately, but are fused to form neutrons. (Thanks Google). This leads me to the question...

I am going to switch gears and talk about neutrinos - those little tiny suckers that go whizzing right through the earth without even noticing it. The question is, can they pass through a neutron star? The reason I ask is this... The flux of solar neutrinos at the earth's surface is on the order of 10^11 per square meter. Now supposing the flux is at least that in the neighbourhood of the neutron star, what happens to all these neutrinos impinging on it's surface? Do they pass on through? I somehow doubt that. Do they crash and burn? If so, how much energy is released by all those neutrinos? Enquiring minds want to know.

Edit: Couldn't wait for your answer, so I asked Google, "Can a neutrino pass through a neutron star?", and guess what, Google pointed me to an Ars article!